In recent years, along with the popularization of personal computers into homes, digital still cameras (hereinafter referred to simply as digital cameras) that enable input of picture image information, such as photographed landscapes and portraits, into a personal computer are rapidly becoming more popular. Additionally, with enhancements in portable telephone functions, portable cameras that include compact imaging modules are rapidly becoming more popular. Additionally, including an imaging module in compact information terminal equipment, such as PDAs (Personal Digital Assistants), is becoming popular.
In such devices that include an imaging function, an image pickup element, such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), is used to provide the imaging function. Recently, advancements in the miniaturization of such image pickup elements have been rapidly increasing. This has resulted in a desire for the main body of such devices and other imaging equipment, such as the imaging lens system, to also be further miniaturized. Additionally, image pickup elements with a larger number of pixels in the same area have been developed in order to achieve higher image quality, which creates a demand for higher resolution lens systems that are still very compact. Japanese Laid-Open Patent Application 2000-258684 describes exemplary single focus imaging lenses for such devices that include only two lens elements.
As stated above, recent image pickup elements are smaller and provide more pixels in a given detector area, which helps meet demands of higher resolution and more compactness that are especially required in imaging lenses for digital cameras. Although considerations of small cost and compactness have been the main considerations for imaging lenses for compact information terminal equipment, such as portable telephones with cameras, such devices have been commercialized with megapixel detectors (detectors that detect one million or more pixels), indicating increasing demand for higher performance in these devices as well. Therefore, development of lens systems with a wide range of applications based on properly balancing considerations of cost, performance, and compactness is desired.
As imaging lenses for compact information terminal equipment having a large number of pixels, conventionally there has been developed a lens system having three lens components, each of which may be a lens element, with at least two lens elements being made of plastic, while the third lens element may be made of plastic or glass. However, in order to meet recent demands for greater miniaturization, a lens that uses a smaller number of lens components and lens elements, but which is equivalent in performance to these conventional lenses, is desired.
Although the lenses described in Japanese Laid-Open Patent Application 2000-258684, referenced above, each have a two-component, two element lens construction, which includes aspheric surfaces, a lens system that is even more compact and higher in performance than this is desired. Because the lateral color aberration tends to become especially large in compact imaging lenses, particularly desired is a single focus lens with well corrected lateral color.